Red emitting luminescent material

ABSTRACT

A red-emitting phosphor comprising an Eu 2+  doped nitridoaluminate phosphor is provided. The red emitting phosphor comprises an emission maximum in the range of 610 to 640 nm of the electromagnetic spectrum.

The invention relates to a red-emitting phosphor, a method for producinga red-emitting phosphor, a use of a red-emitting phosphor in aconversion element and a use of a red-emitting phosphor for theconversion of light.

For devices based on white light emitting diodes (LEDs), especially forbacklighting e.g. of displays, there are few solid-state phosphors thatmeet the requirements of an LED phosphor with emission in the deep redregion of the electromagnetic spectrum. So far, mainly two orange to redemitting phosphors of the formula (Sr,Ba)₂Si₅N₈:Eu²⁺ and(Sr,Ca)AlSiN₃:Eu²⁺ are employed. However, these have considerabledisadvantages with respect to the emission, the coverage of the colorspace, the half-width (FWHM=Full Width at Half Maximum) and the spectralfiltering. In the case of the phosphor (Sr,Ba)₂Si₅N₈:Eu, the emissionwavelength can be shifted from the orange to the red spectral region bysubstituting barium with strontium. However, this substitution reducesthe long-term stability of the phosphor.

Furthermore, the phosphors (Sr)₂Si₅N₈:Eu with dominance wavelengthsabove 605 nm show a significant increase in the half-width, which leadsto a reduction in the efficiency and color saturation and thereforelimits the possible uses of these phosphors. Although the phosphor(Sr,Ca)AlSiN₃:Eu²⁺ already exhibits emission in the deep red spectralrange with dominance wavelengths up to 608 nm, it has a very broademission which extends into the non-visible region of theelectromagnetic spectrum, which reduces the luminescence efficiency ofthis phosphor. Therefore, the demand for a phosphor having emission inthe deep red region of the electromagnetic spectrum, a small half width,and thereby low emission outside the visible region of theelectromagnetic spectrum is of great interest.

WO 2013/175336 A1 and Nature Materials 2014, P. Pust et al.,“Narrow-band red-emitting Sr[LiAl₃N₄]:Eu²⁺ as a next-generationLED-phosphor material” discloses a phosphor of the formulaSrLiAl₃N₄:Eu²⁺ which already has an emission in the deep red region ofthe electromagnetic spectrum and a small half width of about 50 nm.However, the emitted light of this phosphor (λ_(max)=650 nm) shows lessoverlap with the eye-sensitivity curve, especially on itslong-wavelength side, so that the luminescent efficiency of thisphosphor is low.

The luminescence efficiency of this phosphor is about 10% of thetheoretically possible maximum value, which is due to the spectralsensitivity of the eye. In Chemistry of Materials 2014, 26, P. Pust etal., “Ca[LiAl₃N₄]:Eu²⁺—a narrow-band red-emittingnitridolithoaluminate”, a phosphor of the formula CaLiAl₃N₄:Eu²⁺ isshown, emitting in the deep red region of the electromagnetic spectrumand a small half-width of about 60 nm. However, compared toSrLiAl₃N₄:Eu²⁺ the emitted light is shifted even further into the redspectral range, i.e. to higher wavelengths, with an emission maximum atabout 670 nm, which means that this phosphor has an even smaller overlapwith the eye sensitivity curve, especially on its long-wavelength side.

In WO 2015/135888 A1, a red phosphor of the formulaCa_(18.75)Li_(10.5)Al₃₉N₅₅:Eu is described. However, with a maximumemission at 647 nm, this phosphor also shows efficiency losses due tothe small overlap with the eye sensitivity curve on its long wavelengthside.

The object of at least one embodiment of the present invention is toprovide a phosphor which has a deep red emission, exhibits a smallhalf-width and also has a high luminescence efficiency. A further objectis to provide an efficient method for producing a red-emitting phosphor,to provide a use of a red-emitting phosphor in a conversion element anda use of a red-emitting phosphor for the conversion of light.

The objects are achieved by a red-emitting phosphor having the featuresof claim 1, by a method for preparing a red-emitting phosphor having thefeatures of claim 9, by use of a red-emitting phosphor having thefeatures of claims 12 and 13.

It is given a red-emitting phosphor. The phosphor thus has an emissionin the red region of the electromagnetic spectrum.

In an embodiment, the red phosphor comprises a nitridoaluminatephosphor. The nitridoaluminate phosphor is doped with Eu²⁺-atoms.

In an embodiment, the red-emitting phosphor has an emission maximum inthe range of 610 to 640 nm, preferably in the range of 620 and 635 nm,particularly preferably in the range of 625 and 635 nm, for example at626 nm or 634 nm. Thus, the emission is in the deep red spectral rangeof the electromagnetic spectrum. In comparison to the known red-emittingphosphors, the emission maximum of the phosphor according to theinvention is shifted to the shorter-wavelength range of theelectromagnetic spectrum.

In an embodiment, the red-emitting phosphor emits no or only littleradiation outside the visible spectral range. Thus, all or almost allemitted photons are in the sensitivity range of the human eye, whichexcludes or minimizes the efficiency losses by emission in thenon-visible range of the electromagnetic spectrum. This achieves a highluminescence efficiency.

In an embodiment, the red-emitting phosphor has a half-width (Full Widthat Half Maximum, FWHM) of less than 65 nm, preferably less than 60 nm,and comprises the elements Ca, Li, Al, N and Eu.

In an embodiment, the red-emitting phosphor has a half-width (Full Widthat Half Maximum, FWHM) of less than 65 nm, preferably less than 60 nm.For example, the half width may be between 55 nm inclusive and 58 nminclusive. The narrow-band emission significantly improves both colorsaturation and color purity over phosphors with larger half-widths andsimilar dominant wavelengths.

With such a low half-width and an emission maximum in the range of 610nm to 640 nm, the red-emitting phosphor emits only or almost onlyradiation in the visible range of the electromagnetic spectrum. In thisway, no or only slightly loss of efficiency by emission occur in thenon-visible range of the electromagnetic spectrum. In comparison, theknown phosphors (Sr,Ba)₂Si₅N₈:Eu²⁺ have a half-width greater than 90 nm,(Sr,Ca)AlSiN₃:Eu²⁺ a half-width greater than 70 nm, CaLiAl₃N₄:Eu²⁺ ahalf-width of approximately 60 nm and SrLiAl₃N₄:Eu²⁺ a Half width ofabout 50 nm.

As a result of the emission maximum of the red-emitting phosphoraccording to the invention, which is shifted in the shorter-wavelengthrange of the electromagnetic spectrum compared with the knownred-emitting phosphors, and the narrow half-width, the phosphoraccording to the invention has an increased luminescence efficiency incomparison to the known phosphors. The maximum of the eye sensitivity is555 nm. The closer the emission maximum of a phosphor is to 555 nm, thefewer losses that lie outside of the eye sensitivity occur when aconstant half-width of the phosphor is assumed. Thus, with a constanthalf width, the luminescence efficiency increases the closer theemission maximum of a red-emitting phosphor is to 555 nm.

In an embodiment, the luminescence efficiency of the red emittingphosphor is more than 25 percent. In comparison, the luminescenceefficiency of SrLiAl₃N₄:Eu²⁺ is about 10 percent, for CaLiAl₃N₄:Eu²⁺ itis well below 5 percent. Thus, the red-emitting phosphor according tothe invention has a luminescence efficiency which is increased by atleast a factor of 2 in comparison to SrLiAl₃N₄:Eu²⁺ and a luminescenceefficiency which is increased by about a factor of 6 in comparison toCaLiAl₃N₄:Eu²⁺. The high luminescence efficiency makes the red-emittingphosphor according to the invention very interesting for backlightingapplications, in particular for use in a conversion element of an LED.

In an embodiment, the red-emitting phosphor has a dominant wavelength ofλ<620 nm, preferably λ<615 nm. The dominant wavelength is themonochromatic wavelength which produces the same color impression as apolychromatic light source.

In the CIE color space, the line connecting a point for a particularcolor and the point (x=0.333; y=0.333) can be extrapolated to meet theoutline of the space in a maximum of two points. The point ofintersection closer to said color represents the dominant wavelength ofthe color as the wavelength of the pure spectral color at that point ofintersection. The dominant wavelength is therefore the wavelength thatis perceived by the human eye. In general, the dominant wavelengthdeviates from a maximum intensity wavelength. In particular, thedominant wavelength in the red spectral range is at shorter wavelengthsthan the wavelength of maximum intensity.

According to an embodiment, the red-emitting phosphor comprises theelements Ca, Li, Al, N and Eu or consists of these elements.

If the red-emitting phosphor consists of the elements Ca, Li, Al, N andEu, it is possible for the phosphor to have further elements, forexample in the form of impurities, these impurities taken togetherpreferably having at most one weight fraction of the phosphor of at most0.1 per thousand or 10 ppm.

According to an embodiment, the red-emitting phosphor may comprisevarious phases, including the Eu²⁺-doped nitridoaluminate phosphor, orit may consist of one or more further phases and the Eu²⁺-dopednitridoaluminate phosphor. For example, if the red-emitting phosphorconsists of two phases, one corresponding to the Eu²⁺-dopednitridoaluminate phosphor, the Eu²⁺-doped nitridoaluminate phosphor mayhave the same or similar molecular formula as the literature-knownphosphor CaLiAl₃N₄:Eu²⁺ (Chemistry of Materials 2014, 26, P. Pust etal., “Ca[LiAl₃N₄]:Eu²⁺—a narrow-band red-emittingnitridolithoaluminate”), but has a different crystal structure and thusa different arrangement of the atoms. This can be seen from thedifferent X-ray diffraction powder diffractograms of the phosphoraccording to the invention and CaLiAl₃N₄:Eu²⁺ (FIG. 4).

In an embodiment, the red-emitting phosphor comprises one phase of theEu²⁺ doped nitridoaluminate phosphor and a phase of AlN or the redemitting phosphor consists of these phases.

In an embodiment, the red emitting phosphor consists of the Eu²⁺-dopednitridoaluminate phosphor. This means that the red-emitting phosphorconsists of only one phase, namely the Eu²⁺-doped nitridoaluminatephosphor. The red-emitting phosphor may consist of the Eu²⁺-dopednitridoaluminate phosphor, which is present in only one crystalstructure.

It is possible that the Eu²⁺-doped nitridoaluminate phosphor has thesame empirical formula as the phosphor known from the literatureCaLiAl₃N₄:Eu²⁺ (Chemistry of Materials 2014, 26, P. Pust et al.,“Ca[LiAl₃N₄]:Eu²⁺—a narrow-band red-emitting nitridolithoaluminate”),but shows a different crystal structure.

In an embodiment, the red-emitting phosphor is prepared from startingmaterials comprising Li₃N, LiAlH₄, AlN, Ca₃N₂ and EuF₃. The phosphor canalso be prepared consisting of these starting materials. Surprisingly,it has been found that the red-emitting phosphor according to theinvention can be produced from these starting materials with an emissionmaximum between 610 and 640 nm.

In an embodiment, the molar ratio of the starting materials correspondsto the molar composition Ca_(1-x)LiAl₃N₄Eu_(x) with x=0.001 to 0.1. Inthis case, the red emitting phosphor according to the invention or theEu²⁺-doped nitridoaluminate phosphor phase has a different crystalstructure than the known Ca_(1-x)LiAl₃N₄Eu_(x)-phosphor. In comparisonwith the known CaLiAl₃N₄:Eu²⁺-phosphor, the phosphor according to theinvention has no rod-shaped crystals but crystals with octahedralmorphology.

Energy-dispersive X-ray spectroscopy (EDX) measurements show anelemental ratio of the red-emitting phosphor within the accuracy of Cato Al between 1:2 and 1:3.

In an embodiment, the red-emitting phosphor can be excited by radiationin the UV range to the green region of the electromagnetic spectrum. Forexample, the red-emitting phosphor can be excited by radiation having awavelength of 240 nm to 600 nm, preferably 400 nm to 500 nm, for exampleat 460 nm.

The specified embodiments of the red-emitting phosphor can be preparedaccording to the following methods. All features of the red-emittingphosphor are also disclosed for the method and vice versa.

A method is disclosed of preparing a red-emitting phosphor comprising anEu²⁺-doped nitridoaluminate phosphor. The red-emitting phosphorcomprises an emission maximum in the range of 610 to 640 nm of theelectromagnetic spectrum. The method comprises the following methodsteps:

-   A) mixing the starting materials comprising or consisting of Li₃N,    LiAlH₄, Ca₃N₂, AlN and EuF₃,-   B) heating the mixture obtained under A) to a temperature T1 between    900 and 1400° C.,-   C) Annealing the mixture at a temperature T1 of 900 to 1400° C. for    five minutes to 30 hours.

It has surprisingly been found that it is possible to prepare thered-emitting phosphor according to the invention, which has an emissionmaximum in the range from 610 to 640 nm of the electromagnetic spectrumand also a narrowband emission, from the starting materials Li₃N,LiAlH₄, Ca₃N₂, AlN and EuF₃. Thus, it is surprisingly possible toproduce a red-emitting phosphor which has a significantly increasedluminescence efficiency compared to the prior art.

In an embodiment, the starting materials are present as a powder.

In an embodiment, the molar ratio of Li₃N:LiAlH₄ is between 1:10 and1:1, preferably between 1:5 and 1:1, for example at 1:3.

In an embodiment, T1 is between 1100 to 1300° C., for example at 1250°C. or 1125° C. and the annealing in step C) is carried out for 0.5 hoursto 30 hours, preferably for one to 24 hours.

In an embodiment, T1 is at 1250° C. and the annealing in step C) is for0.5 hours to 5 hours, for example, for one hour.

In an embodiment, T1 is 1125° C. and the annealing in step C) is for 15hours to 30 hours, for example for 24 hours.

In an embodiment, after method step C), a further method step follows:

-   D) cooling the mixture to a temperature T2, where room    temperature<T2 <T1. Room temperature is understood to mean 20° C.

In an embodiment, another method step follows after method step D):

-   E) Annealing the mixture at a temperature T2 of 800 to 1300° C. for    five minutes to two hours. Preferably, the annealing is carried out    for five minutes to 60 minutes, more preferably for 10 minutes to 30    minutes. In particular, when process steps D) and E) take place, the    annealing in process step C) can take place for five minutes to two    hours, preferably for five minutes to 60 minutes, particularly    preferably for 10 minutes to 30 minutes.

In an embodiment, T2 is between 800° C. and 1300° C., preferably between900° C. and 1200° C., more preferably between 950° C. and 1100° C., forexample at 1000° C.

In an embodiment, T1=1250° C. and T2=1000° C. The annealing in processsteps C) and E) in this embodiment in each case can last for 10 minutesto 30 minutes, for example for 15 minutes.

In an embodiment, a further method step follows on method step C) or E):

-   F) Cooling of the mixture to room temperature.

In an embodiment, the mixture is cooled to room temperature in processstep F) at a cooling rate of 10 to 400° C. per hour, preferably 30 to300° C. per hour, for example at a cooling rate of 250° C. or 45° C. perhour.

In an embodiment, the cooling of the mixture to T2 in method step D) iscarried out at a cooling rate of 10 to 400° C. per hour, preferably 30to 300° C. per hour.

In an embodiment, method steps B), C), D), E) and/or F) take place undera forming gas atmosphere. Preferably, in the forming gas the ratio ofnitrogen:hydrogen is 92.5:7.5.

In an embodiment, the method steps B), C), D), E) and/or F) take placein a tube furnace.

In an embodiment, the heating in step B) is carried out at a heatingrate of 100 to 400° C. per hour, more preferably from 150 to 300° C. perhour, more preferably from 200 to 250° C. per hour, for example at aheating rate of 250° C. per hour.

In an embodiment, the starting materials are used in a molar ratioAlN:Ca₃N₂:Li₃N:LiAlH₄:EuF₃=1:0.05-0.5:0.01-0.1:0.05-0.5:0.0001-0.01. Thestarting materials are preferably used in a molar ratioAlN:Ca₃N₂:Li₃N:LiAlH₄:EuF₃=1:0.05-0.3:0.03-0.09:0.05-0.4:0.0002-0.001,the starting materials are particularly preferably used in a molar ratioAlN:Ca₃N₂:Li₃N:LiAlH₄:EuF₃=1:0.1-0.2:0.06-0.08:0.1-0.3:0.0003-0.001.

In an embodiment, the molar ratio of the starting materials correspondsto the molar composition Ca_(1-x),LiAl₃N₄Eu_(x) with x=0.001 to 0.1.

The specified embodiments of the red-emitting phosphor can be employedfor the uses mentioned below. All features of the red-emitting phosphorand its method of manufacture are also disclosed for the uses and viceversa.

The use of a red-emitting phosphor to convert light to longerwavelength, red light is provided. By this is meant that light isabsorbed by the red-emitting phosphor and emitted as light having alonger wavelength which is in the red spectral region. The red-emittingphosphor has an emission maximum in the range of 610 nm to 640 nm of theelectromagnetic spectrum.

In an embodiment of the use, the red-emitting phosphor is used toconvert blue light into red light having a longer wavelength. Forexample, the blue light has a wavelength of 400 nm to 500 nm.

The use of a red-emitting phosphor in a conversion element is given. Thered emitting phosphor has an emission maximum in the range of 610 nm to640 nm of the electromagnetic spectrum.

In an embodiment of the use, the conversion element is part of alight-emitting diode (LED).

In an embodiment of the use, the LED comprises a semiconductor chipwhich, in operation, emits blue radiation in a wavelength range from 400nm to 500 nm, for example at 460 nm. A semiconductor chip suitable foremitting blue radiation during operation is based, for example, ongallium nitride or indium gallium nitride.

Preferably, the LED emits white light. In this embodiment, theconversion element may additionally comprise a phosphor which emitsradiation in the green region of the electromagnetic spectrum.

The given embodiments of the red-emitting phosphor can be used in aconversion element of a light-emitting diode.

It is given a light emitting diode. This comprises a semiconductor chipwhich emits blue radiation in the wavelength range from 400 nm to 500 nmduring operation of the component and a conversion element comprising ared-emitting phosphor which comprises an Eu²⁺-doped nitridoaluminatephosphor and which has an emission maximum in the range of 610 nm to 640nm of the electromagnetic spectrum. During operation of thelight-emitting diode, the red-emitting phosphor is set up to convert theradiation emitted by the semiconductor chip into secondary radiationhaving a wavelength between 610 nm and 640 nm.

Due to its high luminescence efficiency the red-emitting phosphor can bepresent in a lower concentration in the conversion element thanpreviously known narrow-band red emitting phosphors, since a lowerradiation intensity is needed to achieve the same efficiency.

A possible embodiment of the conversion element is the embodiment in theform of a potting, wherein the encapsulation encloses the semiconductorchip in a form-fitting manner. Furthermore, the encapsulation on theside walls, which surrounds the semiconductor chip in a form-fittingmanner, can be stabilized, for example, by a housing and is located, forexample, in a recess of such a housing. Materials for potting are knownin the art.

Furthermore, the conversion element can be designed as a conversionlayer. In the conversion layer there is a direct contact between theconversion layer and the semiconductor chip, wherein the thickness ofthe conversion layer is, for example, smaller than the thickness of thesemiconductor chip and, for example, can be formed constant at allradiation exit surfaces.

The conversion element may also take the form of a plate or a foil. Theplate or foil is disposed over the semiconductor chip. These furthervariants of the embodiment of the conversion element do not necessarilycomprise a direct and/or form-fitting contact of the conversion elementwith the semiconductor chip. This means that there can be a gap betweenthe conversion element and the semiconductor chip. In other words, theconversion element is arranged downstream of the semiconductor chip andis illuminated by the emitted radiation of the semiconductor chip.Between the conversion element and the semiconductor chip, a pottingbody or an air gap can then be formed.

Further advantageous embodiments and developments of the invention willbecome apparent from the embodiments described below in conjunction withthe figures.

FIG. 1 shows an emission spectrum of an exemplary embodiment of ared-emitting phosphor in comparison to emission spectra of two knownphosphors,

FIG. 2 shows characteristic properties of a first and a secondembodiment of a red-emitting phosphor in comparison to two knownphosphors,

FIGS. 3 and 4 show X-ray powder diffraction patterns of an embodiment ofa red emitting phosphor using copper-K_(α1)-radiation.

FIG. 1 shows the emission spectrum of a first exemplary embodiment ofthe phosphor according to the invention (curve with the reference symbolIa). In addition, an emission spectrum of the known phosphorCaLiAl₃N₄:Eu²⁺ (curve with the reference numeral IIIa) and an emissionspectrum of the known phosphor SrLiAl₃N₄:Eu²⁺ (curve with the referencenumeral IIa) is shown. The wavelength is plotted in nanometers on thex-axis and the emission intensity in percent on the y-axis.

To measure the emission spectra, the phosphor according to the inventionwas excited with a blue LED having an emission radiation of 460 nm. Thephosphor according to the invention has a half-width of 57 nm and adominant wavelength of 611 nm, the maximum of the emission is 634 nm.Thus, the phosphor of the present invention emits almost only in thevisible region of the electromagnetic spectrum, resulting in an increasein the overlap with the eye sensitivity curve and thus in the reductionof efficiency losses. The known phosphor CaLiAl₃N₄:Eu²⁺ was excited withan emission radiation of 470 nm and the known phosphor SrLiAl₃N₄:Eu²⁺was excited with an emission radiation of 440 nm. As can be seen, theknown phosphor SrLiAl₃N₄:Eu²⁺ has an emission maximum at about 650 nmand the known phosphor CaLiAl₃N₄:Eu²⁺ an emission maximum at about 670nm.

The half-widths of the known phosphors are approximately in the samerange as in the phosphor according to the invention. Due to the emissionmaximum of the phosphor according to the invention, which is shiftedinto the blue spectral range in comparison with the known phosphors, theinventive phosphor has a significantly increased luminescenceefficiency. The phosphor according to the invention thus has anincreased overlap with the eye sensitivity curve, which leads to thereduction of efficiency losses.

The first embodiment of the phosphor according to the invention, whichhas the emission spectrum with the reference Ia in FIG. 1, was preparedas follows: 0.064 mol Ca₃N₂, 0.032 Li₃N, 0.096 mol LiAlH₄, 0.432 mol AlNand 0.00019 mol EuF₃ are homogeneously mixed. The molar ratioAlN:Ca₃N₂:Li₃N:LiAlH₄:EuF₃ is 1:0.148:0.074:0.22:0.00044. Thiscorresponds to a europium content of 0.1 mol % with respect to theamount of Ca in the starting materials. The mixture is transferred to atungsten crucible, which is transferred to a tube furnace. Under aforming gas atmosphere (N₂:H₂=92.5:7.5), the mixture is heated at aheating rate of 250° C. per hour to a temperature of 1250° C. Themixture is annealed for one hour at a temperature of 1250° C., followedby cooling to room temperature with a cooling rate of 250° C. per hour.

FIG. 2 shows characteristic data of the first embodiment (A1) and asecond embodiment (A2) in comparison to the known phosphorsSrLiAl₃N₄:Eu²⁺ and CaLiAl₃N₄:Eu²⁺. λ_(dom) is the dominant wavelength innanometers, λ_(max) is the maximum emission in nanometers, x, y are thecoordinates of the emitted radiation within the CIE standard table(1931), LE is the luminescence efficiency in % and FWHM is thehalf-width in nanometers. The luminescence efficiency is given inpercent and refers to the maximum of the luminescence efficiency at 555nm. At 555 nm, the luminescence is 683 lumens/watt. The data providedwith * are taken from the literature or are calculated from theliterature data. All other data are experimental data of the inventors.The synthesis of the first embodiment A1 is described under with FIG. 1.

The second embodiment of the phosphor according to the invention wasprepared as follows: 9.430 g Ca₃N₂, 1.112 g Li₃N, 3.630 g LiAlH₄, 17.670g AN and 0.158 g EuF₃ are homogeneously mixed. The mixture istransferred to a tungsten crucible, which is transferred to a tubefurnace. Under a forming gas atmosphere (N₂:H₂=92.5:7.5), the mixture isheated at a heating rate of 250° C. per hour to a temperature of 1125°C. The mixture is annealed for 24 hours at a temperature of 1125° C.,followed by a cooling to room temperature with a cooling rate of 45° C.per hour.

FIG. 3 shows two X-ray powder diffraction patterns usingcopper-K_(α1)-radiation. The diffraction angles are given in °2θ-valueson the x-axis and the intensity on the y-axis. The X-ray powderdiffraction pattern provided with the reference I shows the diffractionpattern of the first embodiment of the red-emitting phosphor accordingto the invention, which was synthesized as provided under FIG. 1. TheX-ray diffraction data were recorded by means of a surface samplecarrier on a powder diffractometer (PANalytical Empyrean) withX-Celerator CCD detector in Bragg-Brentano geometry. The X-raydiffraction powder pattern provided with reference II is a simulateddiffraction pattern of the compound of formula SrLiAl₃N₄ based on NatureMaterials 2014, P. Pust et al., “Narrow-band red-emittingSr[LiAl₃N₄]:Eu²⁺ as a next-generation LED-phosphor material”. From theillustrated X-ray powder diffraction patterns it is clear that thered-emitting phosphor according to the invention has a different crystalstructure than the known phosphor of the formula SrLiAl₃N₄:Eu²⁺.

FIG. 4 shows two X-ray powder diffraction patterns usingcopper-K_(α1)-radiation. The diffraction angles are given in °2θ− valueson the x-axis and the intensity on the y-axis. The X-ray powderdiffraction pattern provided with the reference I shows that of thefirst embodiment of the red emitting phosphor according to theinvention, which was synthesized as provided under FIG. 1. The X-raydiffraction data were recorded by means of a surface sample carrier on apowder diffractometer (PANalytical Empyrean) with X-Celerator CCDdetector in Bragg-Brentano geometry. The X-ray powder diffractionpattern provided with the reference III is a simulated compound of theformula CaLiAl₃N₄ based on Chemistry of Materials 2014, 26, P. Pust etal., “Ca[LiAl₃N₄]:Eu²⁺-a narrow-band red-emittingnitridolithoaluminate”. From the illustrated X-ray powder diffractionpatterns it is clear that the red emitting phosphor of the invention hasa different crystal structure than the known phosphor of the formulaCaLiAl₃N₄:Eu²⁺.

The invention is not limited by the description based on the embodimentstherein. Rather, the invention encompasses any novel feature as well asany combination of features, which includes in particular anycombination of features in the patent claims, even if this feature orcombination itself is not explicitly stated in the patent claims orexemplary embodiments.

This patent application claims the priority of German Patent Application10 2015 119 149.0, the disclosure of which is hereby incorporated byreference.

REFERENCE NUMBERS

-   E emission intensity-   Ia, IIa, Iia emission spectra-   nm nanometer-   λwavelength-   A1 first embodiment-   A2 second embodiment-   λ_(dom) dominant wavelength-   λ_(max) maximum emission-   x,y coordinates in the CIE standard table (1931)-   LE luminescence efficiency-   FWHM half-width-   I, II, III X-ray powder diffraction patterns

1. A red-emitting phosphor comprising an Eu²⁺ doped nitridoaluminatephosphor, wherein the red-emitting phosphor comprises an emissionmaximum in the range of 610 to 640 nm of the electromagnetic spectrum.2. Red-emitting phosphor according to claim 1, wherein the red-emittingphosphor has a half-width of less than 65 nm, and the red-emittingphosphor comprises the elements Ca, Li, Al, N and Eu.
 3. Red-emittingphosphor according to claim 1, wherein the red-emitting phosphorcomprises an emission maximum in the range of 620 to 635 nm. 4.Red-emitting phosphor according to claim 1, wherein the red-emittingphosphor comprises a half-width of less than 65 nm.
 5. Red-emittingphosphor according to claim 1, wherein the red-emitting phosphorcomprises the elements Ca, Li, Al, N and Eu.
 6. Red-emitting phosphoraccording to claim 1, wherein the red-emitting phosphor consists of theelements Ca, Li, Al, N and Eu.
 7. Red-emitting phosphor according toclaim 1, wherein the red-emitting phosphor is prepared from startingmaterials comprising Li₃N, LiAlH₄, AlN, Ca₃N₂ and EuF₃.
 8. Red-emittingphosphor according to claim 7, wherein the molar ratio of the startingmaterials corresponds to the molar composition Ca_(1-x)LiAl₃N₄Eu_(x),where x=0.001 to 0.01
 9. Red-emitting phosphor according to claim 1,wherein the red-emitting phosphor comprises a dominant wavelength ofλ<620 nm.
 10. A method of preparing a red-emitting phosphor comprisingan Eu²⁺ doped nitridoaluminate phosphor, wherein the red-emittingphosphor comprises an emission maximum in the range of 610 to 640 nm ofthe electromagnetic spectrum, comprising the steps of: A) mixing thestarting materials comprising Li₃N, LiAlH₄, Ca₃N₂, AlN and EuF₃, B)heating the mixture obtained under A) to a temperature between 900 and1400° C., C) annealing the mixture at a temperature of 900 to 1400° C.for five minutes to 30 hours, F) cooling of the mixture to roomtemperature.
 11. Method according to claim 10, wherein steps B) to F)take place under a forming gas atmosphere.
 12. Method according to claim10, wherein the starting materials are used in a molar ratio ofAlN:Ca₃N₂:Li₃N:LiAlH₄:EuF₃=1:0.05-0.5:0.01-0.1:0.05-0.5:0.0001-0.01. 13.Use of a phosphor according to claim 1, conversion element of an LED.14. Use of a red-emitting phosphor according to claim 1, for theconversion of light into longer-wave, red light.
 15. Red-emittingphosphor according to claim 1, wherein the red-emitting phosphor has ahalf-width of less than 65 nm, and the red-emitting phosphor consists ofthe elements Ca, Li, Al, N and Eu.